UWB (Ultra Wide Band) wireless communication is a method of making communications by using a pulse of a very short duration of no more than one nanosecond (10−9) without using a carrier waveform and the bandwidth is a wide bandwidth spanning several GHz. In a UWB system, a plurality of pulses of no more than 1 ns is transmitted without carrier wave modulation such as cosine wave modulation. Hence, the occupied band is very wide and the spectrum power density is very small. Therefore, there is the characteristic that the effect on other narrowband communications is small and call privacy and secrecy are superior as in the case of a normal spread spectrum communication system.
A UWB signal is known as UWB on account of having an Ultra Wide Band (a bandwidth of several GHz) in comparison with not only a modulated signal such as a BPSK signal but also a normal spread spectrum signal (a bandwidth of several tens of MHz in a 2.4 GHz-band wireless LAN). In comparison with that of a spread spectrum signal (10 milliwatts: 10 mW/MHz or less in a 2.4 GHz-band wireless LAN), the power spectrum density of a UWB signal is markedly low (typically 10 nanowatts for one MHz: not more than 10 nW/MHz), which means that is the UWB signal not subject to interference even when another system coexists, and there is also the advantage that the UWB signal is resistant to interference from the other systems. These advantages are the emphasized features of the conventional spread spectrum signal
In UWB transmission procedure, first a pulse waveform is produced by synchronizing with a frame clock, and second the pulse is time-hopped corresponding to a spreading code, where each user's transmitted signal can be distinguished each other by using orthogonality of spreading codes, that is CDMA or code division multiple access. In addition, a pulse train that is subjected to time hopping in accordance with an input data signal is shifted and not shifted through time d to generate a signal waveform for datum 0 and 1, respectively.
Further, UWB reception makes a correlation between a signal waveform that is received by an RF portion and a pulse train that is formed by means of the same processing as on the transmission side. The peak of the correlation value is used to distinguish data and noise.
UWB pulse transmission includes Documents 1 and 2, for example.
Further, documents related to UWB ranging that uses chirp waveforms include Documents 3 to 11, for example.
Moreover, documents related to multivalued UWB-CDMA that uses modified Hermite waveforms include Documents 3 and 12 to 18, for example.
Further, documents related to transmission power restrictions include Documents 3, 6, and 19 to 22, for example.
Moreover, documents related to the reduction of interference between UWB and an existing signal include Documents 3, 13, 17, and 23 to 32, for example.    Document 1: Nikkei Electronics; pages 137 to 144, Aug. 26, 2002;    Document 2: Nikkei Electronics; pages 95 to 121, Feb. 17, 2003;    Document 3: Ryuji Kohno: “Foundation and development of Impulse Radio UltraWideband (UWB) wireless communications” IEICE Tech. Rep. July 2001; DSP2001-80, SST2001-40 pp 77 to 84;    Document 4: Takeshi Matsumura, Kazuki Eshima, Ryuji Kohno: “Study on TTS intervehicular ranging system using Ultra Wide Band wireless Impulse Radio” ITS2002-6;    Document 5: Tadatomo Sato, Kazuki Eshima, Giuseppe ABREU, Ryuji Kohno: “Study on array antenna using electronic antenna with different frequency characteristic suitable for Ultra Wide Bandwireless communications” IEICE Wireless Communication System Research Academy, May 2002;    Document 6: Gen Marubayashi, Masao Nakagawa, Ryuji Kohno: “Spread spectrum communication and applications thereof”; IEICE;    Document 7: Moe Z. Win, Robert A. Scholtz: “Ultra-Wide BandwidthTime-Hopping Spread-Spectrum Impulse Radio for Wireless Multiple-Access Communications” IEEE TRANSACTION ON COMMUNICATIONS, VOL. 48, NO. 4, APRIL 2000, PP 679 to 691;    Document 8: Yoshiyuki Tomizawa, Ikuo Arai: “Chirp signal pulse compression sublayer radar employing delay correlator” IEICE Journal, pages 113 to 120, 2000-1;    Document 9: James D. Taylor “ULTRA-WIDEBAND RADAR TECHNOLOGY” CRCPRESS;    Document 10: Takashi Yoshida: “Revised radar technology” IEICE Society;    Document 11: Matsuo Sekine: “Radar signal processing technology” IEICE Society;    Document 12: Time Domain Corporation: “Time Modulated Ultra-Wideband for Wireless Applications” http://www.time-domain.com    Document 13: M. Ghavami, L. B. Michael and R. Kohno: “Hermite Function based Orthogonal Pulses for UWB Communications” Proc. Wireless Personal Multimedia. Conference 2001, Aalborg, Denmark, September 2001, pp. 437-440;    Document 14: L. B. Michael, M. Ghavami and R. Kohno: “Effect of Timing. Jitter on Hermite Function Based Orthogonal Pulses for Ultra. Wideband Communication” Proc. Wireless Personal Multimedia Conference 2001, Aalborg, Denmark, September 2001, pp. 441-444;    Document 15: L. B. Michael, M. Ghavami and R. Kohno: “Multiple Pulse Generator for Ultra-Wideband Communication using Hermite Polynomial Based Orthogonal Pulses” Proc. 2002 IEEE Conference on Ultra, Wideband Systems and Technologies, Maryland, USA, May 21-23, 2002;    Document 16: Kazuki Eshima, Kenta Umebayashi, Katsuya Mizutani, Ryuji Kohno, “Study on Impulse Radio Multivalued and multi-user interference removal system”, IEICE Tech. Rep., SS2001-16, CS2001-16, pp. 41-48, April 2001;    Document 17: Tadatomo Sato: “A study on array antenna using electronic antenna with different frequency characteristic suitable for Ultra Wide Band wireless communications” graduation thesis 2001;    Document 18: Shinichi Tachikawa, Gen Marubayashi, “M-arySSMA frequency usage efficiency” IEICE Journal 1990/10 Vol. J73-A No. 10, pages 1678 to 1687;    Document 19: Erick Homier, “Ultra-Wideband Impulse Radio Interference with the Global Positioning System”, Mar. 22, 2000;    Document 20: Ming Luo, Dennis Akos, Michael Koenig, Guttorm Opshang, Sam Pullen and Per Enge, “Testing and Research on Interference to GPS from UWB Transmitters”, Stanford University;    Document 21: The FCC's Part 15 Rules and Regulation and 802.11b emissions http://obelix.umb.es/web/jgomsi/wireless/fcc;    Document 22: L. Cohen, (translated by Yoshikawa et al.) “Time-frequency analysis”, Asakura Syoten, 1998;    Document 23: Robert A. Sclioltz, Moe Z. Winl: “IMPULSE RADIO” Wireless Communications TDMA versus CDMA    Document 24: Ryuji KOHNO: “Principle and Emotion of Ultra Wideband (UWB) Wireless Communications Based on Impulse Radio” TECHNICAL REPORT OF IEICE DSP 2001-80 SST 2001-40(2001-7)    Document 25: Kazuki Eshima, Yoshihiro Hase, Shingo Oomori, Fujinobu Takahashi, Ryuji Kohno, “M-ary UWB System Using Walsh Codes,” IEEE Conference on Ultra Wideband Systems and Technologies 2002 (UWBST2002), Wyndham Baltimore Inner Harbor (USA), (2002-5)    Document 26: Kazuki Eshima, Yoshihiro Hase, Shingo Oomori, Fujinobu Takahashi, Ryuji Kohno, “Performance Analysis of Interference between UWB and SS Signal,” 2002 IEEE Seventh International Symposium on Spread Spectrum Techniques and Applications (ISSSTA2002), Prague, (Czech Republic), (2002-9)    Document 27: Kazuki Eshima, Katsuya Mizutani, Ryuji Kohno, Yoshihiro Hase, Shingo Oomori, Fujinobu Takahashi, “A Study on M-ary UWB Impulse Radio and An Effect of It's Time Jitters,” IEICE General Conferences SB-3-3, pp. 569-570 (2001-9)    Document 28: Kazuki Eshimna, Katsuya Mizutani, Ryuji Kohno, Yoshihiro Hase, Shingo Oomori, Fujinobu Takahashi, “Comparison Ultra-Wideband (UWB) Impulse Radio with DS-CDMA and FH-CDMA “The 24th Symposium on Information Theory and Its Applications (SITA2001). pp. 803-806 (2001-12);    Document 29: Kazuki Eshimna, Yoshihiro Hase, Shingo Oomori, Fujinobu Takahashi, Ryuji Kohno, “A Study of Performance Analysis of Interference between UWB and SS signals” Technical Report of IEICE RCS 2001-246 pp. 15-20(2002-03)    Document 30: Kazuki Eshima, Yoshihiro Hase, Shingo Oomori, Fujinobu Takahashi, Ryuji Kohno, “Effect of Interference between UWB System and Other Radio Systems” IEICE General Conference, A-5-18, pp. 200 (2002-3)    Document 31: Kazuki Eshima, Yoshihiro Hase, Shingo Oomori, Fujinobu Takahashi, Ryuji Kohno, “A Study of Performance Analysis of Interference between Dualcycle UWB and SS signals” IEICE General Conference, A-5-10, pp 106 (2002-9)    Document 32: Kazuki Eshima, Yoshihiro Hase, Shingo Oomori, Fujinobu Takahashi, Ryuji Kohno, “A Study on Performance Analysis of Interference between Dualcycle UWB and SS Signals” The 25th Symposium on Information Theory and Its Applications (SITA2002), pp 295-298(2002-12)
Document 2 proposes, for technological problems that UWB possesses, a reduction of radio interference with other wireless systems, conformity with the radio wave regulations in respective countries, the suppression of transmission errors of reflected waves from walls and objects and so forth (multipath countermeasure), the uninterrupted implementation of communications between a plurality of devices (multi-access), a reduction of mounting costs of a UWB wireless circuit portion and so forth.
Among such proposed measures, the problem of radio interference is an important matter in cases where UWB is applied to consumer electronics and so forth. For such radio interference, the U.S. FCC (Federal Communication Committee), for example, regulates UWB transmission outputs.
Therefore, the present invention solves the earlier-mentioned conventional problems, an object thereof being to reduce radio interference with other wireless systems in UWB communication and to form a transmission signal with a desired frequency characteristic.